A thermal power plant generates power by driving a power generating device using heat of combustion acquired by burning mainly fossil fuel, and there are various devices according to combinations of fuel and power generating devices. For example, there are devices such as: a device that generates power by driving a steam turbine using steam generated by heat of combustion acquired by burning coal, heavy oil, or the like in a boiler; a gas turbine power generator that generates power by driving a gas turbine using combustion air acquired by burning a mixture of air compressed by a compressor and fuel in a burner; and a combined cycle power generator that drives a steam turbine using steam generated in an exhaust heat recovery boiler by using exhaust gas burned in a gas turbine.
A gas turbine decreases in output in a case where atmosphere temperature is high, such as summer, because air density in the atmosphere is low to cause a mass flow rate of air taken and compressed by a compressor to decrease. In addition, increase in the number of years operated deteriorates output due to aging degradation.